Riser cracking of solvent extracted gas oil

ABSTRACT

A GAS OIL PASSED THROUGH A SOLVENT EXTRACTION ZONE TO SEPARATE AN AROMATICS-RICH EXTRACT FRACTION FROM AN AROMATICS-LEAN RAFFINATE FRACTION, EACH HAVING A BOILING RANGE SUBSTANTIALLY AS WIDE AS THE FEED GAS OIL. A FLUIDIZED MIXTURE OF ZEOLITE AND NONZEOLITE CRACKING CATALYST IS CONTINUOUSLY PASSED UPWARDLY THROUGH AN ELONGATED CRACKING REACTOR WHICH DOES NOT CONTAIN ADDED HYDROGEN. THE AROMATICS-LEAN RAFFINATE FRACTION IS CONTINUOUSLY CHARGED TO THE REACTOR AT A POSITION CLOSE TO THE BOTTOM THEREOF WHILE THE AROMATICS-RICH EXTRACT FRACTION IS CONTINUOUSLY CHARGED TO THE REACTOR AT A POSITION MORE REMOTE FROM THE BOTTOM THEREOF.

April 4, 1972 E-J DOBER ETAL RISILR CRACKING OF SOLVENT EXTRACTED GAS OIL Filed July 23, 1970 Smm w .www

United States Patent O 3,654,137 RISER CRACKING F SOLVENT EXTRACTED GAS OIL Edward J. Doher, Pittsburgh, and Robert W. Koch, Verona, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa.

Filed July 23, 1970, Ser. No. 57,587 Int. Cl. Cg 11/18 U.S. Cl. 208--87 8 Claims ABSTRACT 0F THE DISCLOSURE A gas oil is passed through a solvent extraction zone to separate an aromatics-rich extract fraction fromI an aromatics-lean raffinate fraction, each having a boiling range substantially as wide as the feed gas oil. A iluidized mixture of zeolite and nonzeolite cracking catalyst is continuously passed upwardly through an elongated cracking reactor which does not contain added hydrogen. The aromatics-lean ratlinate fraction is continuously charged to the reactor at a position close to the bottom thereof while the aromatics-rich extract fraction is continuously charged to the reactor at a position more remote from the bottom thereof.

The present invention relates to cracking of a gas oil hydrocarbon which prior to cracking is passed through an aromatics extraction Zone to seperate an aromaticsrich extract fraction from an aromatics-lean rafiinate fraction.

The present invention relates to cracking in a nonhydrogen atmosphere of aromatics-rich and aromaticslean fractions of a gas oil hydrocarbon in the presence of a uid noncrystalline, i.e., amorphous, silica alumina nonzeolite cracking catalyst and a fluid crystalline aluminosilicate zeolite cracking catalyst, respectively. According to the prior art methods wherein cracking was carried out in the presence of hydrogen under both hydrogenation and cracking conditions, it was found that high boiling polynuclear aromatics are hydrocracked more eiciently over a nonzeolite catalyst than over a zeolite catalyst, 'while the lower boiling monoaromatics are hydrocracked more efficiently over a zeolite catalyst. Therefore, the prior art teaches that in hydrocracking a wide boiling range gas oil as much as possible of the higher boiling (polynuclear or fused ring) aromatics should be concentrated in a stream fed to a nonzeolite catalyst chamber while as much as possible of the low boiling aromatics should be concentrated in a stream fed to a zeolite catalyst chamber. According to the prior art teaching, it would appear that distillation of the wide range gas oil feed into a light gas oil fraction and a heavy gas oil fraction would be an effective means for preparing the feed to the two zones. However, in accordance with the present invention we have found that more eiiicient cracking in a zeolite zone occurs when a lowaromatics feed having the same wide boiling range as the full range gas oil is charged to the zeolite chamber than if the same feed is diluted with a light gas oil.

In accordance with the present invention which relates to cracking in a nonhydrogen atmosphere, it has been found that after solvent extraction of a wide-boiling range gas oil hydrocarbon stream to produce an aromatics-rich extract stream for charging to a nonzeolite cracking chamber and an aromatics-lean raffinate stream for charging to a zeolite cracking cham'ber, with the extract 3,654,12ril Patented Apr. 4, 1972 ICC and raffinate streams each having about the same wideboiling temperature range as the feed gas oil, the lowboiling aromatics fraction in the extract stream does not exert its expected effect in the process based upon the experience of the prior art in hydrocracking. After conventional solvent extraction of a gas oil the extract fraction is relatively rich in aromatics and because of its wide boiling range it includes both high-boiling polynuclear aromatics and lower-boiling mononuclear aromatics, while the raffinate fraction is relatively lean in aromatics but still contains a substantial quantity of aromatics which, because of the wide boiling range of the process, includes both high-boiling polynuclear aromatics and lower-boiling mononuclear aromatics. Based upon the teaching of the prior art with respect to hydrocracking it would be expected that the advantage of the solvent extraction operation is to remove the high-boiling polynuclear or fused ring aromatics from the raffinate feed to the zeolite cracking chamber, while the removal of lower boiling mononuclear aromatics, if unavoidable, is not desirable in the hydrocracking operation and for best results, in the zeolite cracking chamber, particularly, the lower boiling aromatics which were removed and are in the extract phase which is destined for the nonzeolite chamber should be fractionated from the extract phase and added to the raliinate feed to the zeolite cracking chamber.

It is a surprising discovery in accordance with the present invention in regard to cracking in a non-hydrogen atmosphere that, following the aromatics extraction step, the removal of the light gas oil fraction from the extract phase destined for the nonzeolite chamber and the addition thereof to the ratlinate feed to the zeolite chamber has a deleterious eect in the zeolite cracking operation in regard to both total conversion and gasoline yield, because this is contrary to the experience of the prior art in regard to hydrocracking. Therefore, the dilution of the wide boiling range ranate feed containing polynuclear aromatics with light gas oil which is relatively more rich in mononuclear aromatics had an adverse effect upon cracking eiciency in the zeolite cracking zone. As stated, this effect is unexpected in view of the prior art experience in hydrocraoking which indicates that enrichment of the feed to the zeolite zone with mononuclear aromatics and dilution of polynuclear aromatics is beneficial. This effect also shows an advantage in solvent extraction as a method for feed preparation over simple fractionation of a full range gas oil into two nearly equal fractions; one fraction comprising mostly Ilight gas oil feed for the zeolite zone and the other fraction comprising mostly heavy gas oil feed for the nonzeolite zone. The simple fractionation method concentrates nearly the entire light gas oil fraction in the feed for the zeolite zone in contrast to the experience of the present invention which shows an adverse effect in said zone upon increasing the concentration of light gas oil therein.

The above-described discovery is not only surprising in regard to the prior art teaching regarding hydrocracking but is also surprising in regard to experience in the prior art concerning cracking of gas oil in a non-hydrogen atmosphere in the presence of a zeolite catalyst. It has been the experience of the non-hydrogen zeolitic cracking art that the higher boiling aromatics in general were deleterious feed constituents while lower-boiling aromatics were advantageous feed constituents for gasoline production. The reason is that higher boiling aromatics, such as bicyclics, do not crack easily and tend to be absorbed upo on a zeolite catalyst to lower its activity. Unlike monocyclics, which crack easily in the presence of a zeolite catalyst, the higher boiling aromatics tend to polymerize to form coke. In contrast to the present invention, the prior art experience would tend to indicate that dilution of a wide boiling ranate feed to a zeolite cracking zone with light gas oil would enhance cracking efficiency in said zone.

It has been found that in a combination non-hydrogen cracking process utilizing both zeolite and nonzeolite catalyst the transfer of the light gas oil from the extract phase to the raffinate phase induces more than a compensating rise in activity in the nonzeolite chamber to overcome the loss of activity in the zeolite chamber. In the combination process, a full range gas oil is solvent extracted to produce a wide boiling range aromatics-rich extract phase, which is more advantageously cracked inthe presence of a nonzeolite catalyst than a zeolite catalyst, and to produce a wide boiling range aromatics-lean raffinate phase which is more advantageously cracked in the presence of a zeolite catalyst than a nonzeolite catalyst. When the light gas oil fraction is separated from the extract phase feed to the nonzeolite cracking chamber and blended with the raflinate phase feed to the zeolite cracking chamber, the gasoline yield in the zeolite cracking chamber is reduced. However, the gasoline yield in the nonzeolite chamber is increased by more than a compensating amount so that the gasoline products from the zeolite and nonzeolite cracking chambers are blended, a higher gasoline yield, a higher octane number and a higher total conversion are achieved than in a similar combination process except that the light gas oil fraction is not removed from the extract phase feed to the raflinate phase.

In an advantageous embodiment both a zeolite and nonzeolite catalyst are charged in admixture to the bottom of a transfer line or riser cracker. The aromatics-lean wide boiling range raffinate feed is charged to the elongated transfer line cracker relatively close to or at the bottom thereof and will tend to react primarily with the zeolite portion of the catalyst, which is considerably more reactive than the nonzeolite portion of the catalyst. The wide boiling range aromatics-rich extract feed is charged to the transfer line cracker at a position relatively more remote from the bottom of the cracker and will tend to react primarily with the nonzeolite catalyst since the more reactive zeolite catalyst will have been substantially deactivated by its earlier reaction. In this manner, the aromatics-lean raffinate advantageously reacts primarily with the zeolite catalyst while the aromatics-rich extract advantageously reacts primarily with the nonzeolite catalyst. In an advantageous embodiment, the light gas oil fraction is preremoved from the extract phase and charged upstream in the reactor, for example, together with the aromaticslean raffinate stream. Since light gas oil is more refractory than heavy gas oil, this light gas oil fraction will advantageously have a longer time to remain in the reactor and will advantageously have a preferential opportunity to react with the more reactive zeolite catalyst than if it were charged to the reactor together with the remaining extract stream.

In all cracking zones of this invention, cracking occurs without added hydrogen at a temperature of about 850 F. to 1100 F., or more. The preferred range is 880 F. to 1000 F. The total pressure can vary Widely and can be, for example, to 50 p.s.i.g., or preferably 20 to 30 p.s.i.g. In the zeolite and nonzeolite xed fluid bed chambers of FIGS. 1 through 4, space velocities of 2 to l2 W/H/W can be employed.

The full range gas oil feed to the process of the invention can have an I.B.P. of 450 F. to 500 F. and an E.P. of 1000o to 1050 F. The material referred to herein as light gas oil, such as the material which is removed from the extract phase and added to the raffinate phase, can have a boiling range of 450 to 650 F. Heavy gas oil therefore will have a boiling range from 650 to 1000 or 1050 F.

The light gas oil fraction can slightly overlap the heavy gas oil fraction in which case its E.P. will be about 670 F. The solvent used for aromatics extraction in the tests described below was furfural.

The cracking operation with both zeolite and nonzeolite catalyst occurs Without hdrogen addition to the reactor and therefore occurs without nickel or other catalytic hydrogenation metal on the catalyst. Since the cracking atmosphere does not contain hydrogen the aromatic rings are not saturated and are difficult to crack, which accounts for the basic distinction between the present process and hydrocracking.

FIG. l shows a simple process for fluid fbed cracking with a nonzeolite catalyst. A full range gas oil as described at A in the data of Example 1 is charged through line 10 to liuid nonzeolite catalyst cracking chamber 12. An effluent stream as described at I in the data of Example 3 is recovered through line 14 while a portion of the eiuent is recycled through line 16.

FIG. 2 shows a simple process for fluid bed cracking with a zeolite catalyst. A full range gas oil as described at A in the data of Example 1 is charged through line 18 to -uid bed zeolite catalyst cracking chamber 20. An effluent stream as described at K in the data of Example 3 is recovered through line 22 while a portion of the efliuent is recycled through line 24.

In the process scheme of FIG. 3 a full range gas oil as described at A in the data of Example 1 is charged through line 56 to extraction zone 58 utilizing furfural as a solvent from which zone a low aromatics raffinate is recovered as described at D in the data of Example l through line 60 and a high aromatics extract as described at E in the data of Example 1 through line 62. The raffinate in line 60 is charged to reactor 64 containing a Iiuid bed of zeolite catalyst which discharges an eliluent stream through line 66 as described at I in the data of Example 2, a portion of which is recycled through line A68. The high aromatics extract in line 62 is charged to huid bed nonzeolite catalyst reactor 70 from which an efliuent stream as describe-d at H in the data of Example 2 is discharged through line 72, a portion of which is recycled through line 74. The individual efiiuents in lines 66 and 72 can be removed from the system through lines 67 and 73, respectively, and can be individually utilized as sources of leaded or unleaded gasoline stocks, or the two entire efiiuent streams can be merged in line 75 to provide a total process product as described at M in the data of Example 3.

In FIG. 4 a full range gas oil as described at A in the data of Example 1 is charged to an aromatics extraction unit 28 utilizing furfural as a solvent from which unit a low aromatics raffinate fraction is removed through line 30 while a high aromatics extract is removed through line 32 and passed to a distillation zone 34. Zone 34 discharges a light gas oil extract fraction through line 36 which blends with the low aromatics rainate in line 30 to produce the feed in line 38 as described at B in the data of Example 1 which is charged to the uid zeolite catalyst bed reactor 40 having recycle line 42 and eiiiuent line 44 whose composition is shown at G in the data of Example 2. Distillation zone 34 discharges a heavy gas oil extract efuent through line 46 as described at C in the data of Example 1 which is charged to nonzeolite fluid catalyst bed reactor having a recycle line 50 and a discharge line 52 containing an efuent stream as described at F in the data of Example 2. The eiuents from lines 44 and 52 can be removed from the system through lines 45 and 53, respectively, and can be used as individual sources of leaded or unleaded gasoline stocks or the two entire eluent streams can be merged in line 54 to produce a combined product as described at L in the data of Example 3.

Following are the operating conditions employed for the FCC zeolite and nonzeolite reactors shown in FIGS. 1 through 4.

2 Using zeolite catalyst.

In the embodiments of FIGS. 1 through 4, the catalyst is utilized as a dense iluid bed with zeolite and nonzeolite catalyst confined to separate reactors and preferably free of each other. The embodiment of FIG. 5 shows iiuidized catalyst transfer line cracking wherein fresh or regenerated iluid catalyst is continuously passed as a disperse fluid phase upwardly through elongated transfer line reactor 76, entering the bottom of the reactor through line 7-8 and discharging through line `84, with very little catalyst inventory Within the reactor. The catalyst feed comprises zeolite catalyst admixed with a smaller amount of nonzeolite catalyst. Less preferably, the zeolite and nonzeolite catalysts can be admixed in about equal proportions or the nonzeolite catalyst can be in preponderant amount. The feed passing to the bottom of the transfer line through line 80 can comprise rafiinate stream D from line 60 of FIG. 3 or the feed can comprise raiiinate plus light extract stream B from line 38 of FIG. 4 while the feed entering the upper portion of the transfer line through line 82 which is relatively more remote from the inlet of the transfer line than is line 80 can comprise extract stream E from line A62 of FIG. 3 or heavy extract stream C from line 46 of FIG. 4. The feed entering through lower inlet line 80 will react with the more reactive zeolite catalyst reserving the less reactive nonzeolite catalyst for reaction with the feed entering through li-ne 82, whereby the process of FIG. 5 is analogous to the processes of FIGS. 3 and 4. Gasoline-containing product and catalyst are removed from the top of the transfer line through line 84. Catalyst is separated from hydrocarbon, regenerated and recycled. In the system of FIG. 5, the raffinate phase feed is greater in volume than the extract phase feed and is advantageously in the reactor for a longer period of time, but the longest residence time a much more effective distribution of aromatics between two phases than could be achieved by simple fractionation into relatively high and low boiling fractions. For example, in accordance with the present invention, the extract commonly contains at least twice the concentration of aromatics as the raffinate. More commonly, the extract contains 3, 4 or 5 times and more aromatics than the raffinate. Any known aromatics ysolvent can be employed for the extraction. Solvents known in the art include methanol, ethanol, phenol, furfural, ethylene glycol, monomethyl ether, acetonitrile, sulfur dioxide, etc. The solvents resolve a full range gas oil into a high aromatics extract phase and a low aromatics raffinate phase, each phase having substantially the full boiling range of the feed gas oil and each phase tending to contain monoaromatics in its lower boiling portion and polynuclear or fused ring aromatics in its higher boiling portion. This type of separation is contrasted with distillation of a full range gas oil fraction into two equal phases in which case the amount of aromatics are about equal in the two phases with the monoaromatics tending to be concentrated in the lower boiling 4fraction and the polynuclear or fused ring aromatics tending to be concentrated in the higher boiling fraction. The type of aromatics distribution achieved by distillation is not equivalent to the type of aromatics distribution achieved by solvent extraction in accordance with the discovery of this invention because under the diS- tillation -method of 4aromatics distribution the heavy gas oil phase containing most of the polynuclear aromatics is charged to the nonzeolite catalyst chamber leaving the light gas oil phase containing substantially most of the monoaromatics in the feed for the zeolite catalyst chamber, Whereas it has now been discovered that dilution of a wide boiling range raiiinate feed to a zeolite cracking zone with light gas oil performs a deleterious effect upon gasoline yields in the zeolite cracking zone.

The following examples present typical feed stock data and actual and mathematical model yields based upon correlations from many feeds for the described processing schemes.

EXAMPLE 1 The following table presents the properties of the FCC feedstocks referred to in FIGS. 1 through 4 of the drawings.

PROPERTIES OF THE FCC FEEDSTOCKS REFERRED TO IN FIGS. l THROUGH 4 Drawing designation A B C D E Catalyst in unit where charged Nonzeollitre Zeolite Nonzeolite. Zeolite Nonzeolite.

or zeo i e.

Name of stock. Full range Rainate-l- Heavy Raiinate. Full range gas 011. light extract. extract.' extract.

Gravity: .API 239 30 5 Sulfur: wt. pereent. Nitrogen: wt. percent Aniline point:

STM:

90, Fraction light gas oil (B.P. below Mean avgfboiling point, F 761 Fraction aromatics 0.23

EXAMPLE 2 The following table describes the individual yields of the FCC units referred to in FIGS. 1 through 4 of the traction in accordance with the present invention produces drawings.

INDIVIDUAL FCC YIELDS REFERRED TO IN FIGS. 1 THROUGH 4 Drawing designation F G H I Catalyst type Nonzeolite.. Zeolite Nonzeolite.. Zeolite. Feedstock Heavy Raffinate-i- Full range Ranate.

extract. light extract. extract. FCC yields:

Conversion: volume percent.. 66.9 85.7 64.2 89.6

Debutanized gasoline: vol 44 42.6..- 64.3

percent Cri-gasoline: vol. percent 35.7... 34.2. 49.2

Cir-CF: vol. percent 8.8 84..... 15.1.

C4-C4=: vol. percent.. .6 12.3.... 12.0.

Ca-CF: vol. percent 9.5 12.3.. 9.5.... 13.1.

C2 and ltr :weight percent 5.5 4.4- 5.6. 4.4.

Coke: weight percent 15.2 7.4 13.5.... 7.2.

Motor, clear 79.2 75.9..-. 79.0.. 74.9.

Research, clear 94.4 91.8 94.4 89.9.

The above data show that low aromatics rafiinate stream I from the zeolite reactor exhibits a greater total conversion and a greater conversion to debutanized gaso- 20 line, but with lower octane numbers, as compared to stream K, described below, which relates to treatment of a full range feed with zeolite only. On the other hand, the above data show that high aromatics extract stream H from the nonzeolite reactor exhibits a lower total con- 25 version and a lower conversion to debutanized gasoline, but with comparable octane numbers, as compared to stream J, described below, which relates to treatment of a full range feed with nonzeolite catalyst only.

EXAMPLE 3 full range extract is distilled to remove the light gas oil (450 to 650 F.) fraction therefrom to produce a heavy extract having no light gas oil, and the removed light gas oil is added to the raiiinate to produce a raflinate plus light extract stream, the gasoline yield from the extract was increased from 42.6 to 44.4 volume percent while the gasoline yield from the raflinate was decreased from 64.3 to 61.3 volume percent. It is seen that removal of the light gas oil from the extract increased Igasoline yield from that stream and the addition of the light gas oil to the rainate stream decreased gasoline yield from that stream. This effect is surprising since the prior art teaches in regard to hydrocracking that it is the transfer of only high boiling aromatics to the raffinate feed to a zeolite cracking reactor which is detrimental and that lower molecular weight monoaromatics are advantageously COMBINED FCC YIELDS REFERRED TO IN FIGS. l THROUGH 4 Drawing designation J K L M Zeolite FCC run:

Percent of full range gas 100 72.4 63.9.

oil change. Fraction charged Full range Ratlinate+ Ratlnate.

gas oil. light extract. N onzeolite FCC run:

Percent of full rango gas 100 27.6 36.1.

oil change. Fraction charged Full range Heavy cx- Extract gas oil. tract. Combined FCC yields:

Conversion: vol. percent 69.5 79.2 80.5 80.4. Debutanized gasoline: vol. 48.2 55.7 56.7 56.5.

percent. Cri-gasoline: vol. percent-.- 37.2 44.7 44.4. 43.8. C5-C5=: vol. percent 11. 11.0.... 12 2 12.7. C4C4=z vol. percent 15.3-- 9 Ca-Ca=: vol. percent 10.1- .8.

C2 and ltr.: weight percent.. 4.1 Coke: weight percent 9.1 Motor, clean... Research, clear An important feature indicated in the above data is that stream M which is the result of treatment with both zeolite and nonzeolite catalyst exhibits a higher total conversion and a higher conversion to debutanized gasoline than stream K which is the result of treatment of the total feed with zeolite catalyst even though stream I shows that treatment of any portion lof the feed with a nonzeolite catalyst Would be expected to reduce both total conversion and conversion to debutanized gasoline.

A further highly important feature of the above data is the showing that the unexpectedly high total conversion and conversion to debutanized gasoline as well as octane numbers exhibited by stream M are further enhanced in stream L, which is the blended product of FIG. 4. In ac- 70 cordance with the present invention, with special reference to FIG. 4, it has been found that the light gas oil portion of the extract stream has a marked effect upon gasoline yield in both the zeolite and nonzeolite chambers. Referring to the data in Example 2, it is 'seen that when the 75 transferred from a nonzeolite cracking zone feed to a zeolite cracking zone feed to improve efliciency in said zeolite zone.

EXAMPLE 4 The following data illustrate that the lar-ge difference in aromatics concentration in raflinate and extract streams from solvent extraction is not achieved through distillation of the feed. The first two columns of the following data show zeolite cracking feed stocks having large differences in mean average boiling point but relatively minor differences in aromatics content. The 'second two columns of the following data show zeolite cracking feed stocks having smaller differences in mean average boiling point but greater differences in aromatics content. The data therefore indicate that distillation `of a cracking feed into fractions of Widely different mean average boiling points will not necessarily produce wide differences in aromatics concentration.

High light Low light High Low gas oil gas oil aromatics aromatics in feed in feed in feed in teed Feed preparation (1) (l) (2) (i) Gravity: API 82. 4 25. 7 14. 9 27. 6 Sulfur: Wt. percent 0. 14 0.79 0.41 0. 27 Nitrogen: wt. percent 0. 003 0.076 0. 053 0.047 ASTM:

10%, 565 595 696 807 50%, F- 583 773 788 850 90%, 632 969 865 923 Fraction light gas oil 0.928 0.210 0. 067 0. Mean average B.P., F 588 749 777 854 Fraction aromatics 0.128 0.194 0. 376 0.171 Total recycle: vol. percent 2. 4 2. 6 2.6 2. 5 Catalyst to oil ratio (total feed) 7. 3 8. 1 8. 2 8.0 Space velocity: W/H/W (total feed) 6.04 6. 05 9. 90 9.85 Catalyst type Zeolite Zeolite Zeolite Zeolite Activity, Kellogg 2 hr 38. 6 38. 6 40. 40. 9 Carbon on regenerated catalyst: percent 0.27 0.33 0.37 0. 37 Reactor temp.: F 878 S79 910 910 Dispersion steam: wt. percent (total feed) 5. 70 6.70 G. 40 7.10 Reactor press: p.s.i.g 25.1 25. 2 25.1 25. 1 Conversion: vol. percent 74.7 70. 7 61. 1 76.9 Debutanized gas: vol. percent 59. 8 54. 5 47. 7 60.7 Cui-gasoline: vol. percent 47.0 43. 2 41. 1 49. 5 C5-O5=: vol. percent 12.8 11.3 6. 6 11. 2 C4-C4=: vol. percen 15. 4 13. 7 10.5 14. 5 C3-C3=: vol. percent- 8. 2 8. 0 7. 5 9.9 C2 and ltr.: wt. percent 2. 3 3.1 3. 8 3. 8 Coke: Wt. percent 3.8 7. 4 7. 9 6. 0

1 Not solvent extracted. 2 Solvent extracted.

The cracking data presented in the above table show that great differences in feed aromatics concentration, regardless of average boiling point of the feed, have a much greater effect upon total conversion and gasoline yield in a zeolite reactor than do great differences in average boiling point of the feed accompanied by smaller variations in aromatics content.

EXAMPLE 5 Data were taken to illustrate the criticality to the present invention of employing an amorphous nonzeolite catalyst chamber in conjunction with a zeolite catalyst chamber, rather than employing two separate zeolite catalyst chambers. The data relate to a process as shown in FIG. 3, except that chamber 70 contains a zeolite catalyst rather than a nonzeolite catalyst and the operating conditions for a zeolite chamber as presented above were adopted, while chamber 64 continues to contain a zeolite catalyst. The feed stock and operating conditions are otherwise unchanged from those used in the process of FIG. 3. The following data show the product characteristics based upon a raffinate feed as described above to reactor 64 and the product characteristics based upon a full range extract feed as described above to reactor 70.

Catalyst type (l) (1) Fcedstock (2) FCC yields:

Conversion: vol. percent 89.6 65.8 Debutanized gasoline: vol. percent 64. 3 33. 4 Cyl-gasoline: vol. percent 49. 2 29. 2 C5-C5=: vol. percent 15.1 4. 2 Ct-Ci vol. percent 21,0 11.7 C3C3=: vol. percent 13. l 13. 5 C2 and ltr.: wt. percent 4. 4 4.0 Coke: wt. percent 7. 2 17. 8 Motor, clear 74. 9 76.0 Research, clear 89. 9 92. 0

1 Zeolite. 2 Ratlinate.

3 Full range extract.

The following data show the characteristics of the combined feed from the two zeolite reactors.

Zeolite FCC runs:

Percent full range gas oil charged 63. 9 36. 1 Fraction charged Rafiinate Extract Combined FCC yields: 81 o Conversion: vol. percent Debutanized gasoline: vol. percent.. Cri-gasoline: vol. percent C5-C5=z vol. percent Comparing the product characteristics presented above of the combined product stream from two zeolite reactors with the product characteristics of the combined product stream M from the process of FIG. 3, it is seen that use of both a zeolite and a nonzeolite catalyst chamber rather than two zeolite catalyst chambers results in a considerably higher gasoline yield, a higher octane number gasoline product, and a lower coke yield.

We claim:

1. A process for cracking a feed gas oil without added hydrogen comprising passing said gas oil to an aromatics extraction zone, separating in said zone an aromaticsrich extract fraction from an aromatics-lean rainate fraction each having a boiling range substantially as wide as the feed gas oil, continuously passing a iiuidized mixture of zeolite and nonzeolite cracking catalysts upwardly through an elongated cracking reactor, continuously charging isaid wide boiling range aromatics-lean rafinate fraction to said reactor at a position relatively close to the bottom of said reactor and continuously charging said aromatics-rich extract fraction to said reactor at a position relatively more remote from the bottom of said reactor.

2. The process of claim 1 wherein the concentration of aromatics in said aromatics-rich extract fraction is at least about twice as high as the concentration of aromatics in said aromatics-lean rainate fraction.

3. The process of claim 1 wherein the concentration of aromatics in said aromatics-rich extract fraction is at least about three times as high as the concentration of aromatics in said aromatics-lean raiiinate fraction.

4. The process of claim 1 wherein said catalyst mixture contains zeolite cracking catalyst in greater amount than nonzeolite cracking catalyst.

5. A process for cracking a feed gas oil without added hydrogen comprising passing said gas oil to an aromatics extraction zone, separating in said zone an aromaticsrich extract fraction from an aromatics-lean raiiinate fraction each having a boiling range substantially as wide as the feed gas oil, distilling said aromatics-rich extract fraction to separate a light gas oil extract fraction from a heavy gas oil extract fraction, continuously passing a iiuidized mixture of zeolite and nonzeolite cracking catalysts upwardly through an elongated cracking reactor, continuously charging said wide boiling range aromaticslean raflinate fraction and said light gas oil extract fraction to said reactor at a position relatively close to the 11 bottom of said reactor and charging said heavy-gas oil extract fraction to said reactor at a position relatively more remote from the bottom of said reactor.

6. The process of claim 5 wherein the concentration of aromatics in said aromatics-rich extract fraction is at least about twice as high as the concentration of aromatics in said aromatics-lean rafnate fraction.

7. The process of claim 5 wherein the concentration of aromatics in said aromatics-rich extract fraction is at least about three times as high as the concentration of aromatics in said aromatics-lean rafnate fraction.

8. The process of claim 5 wherein said catalyst mixture contains zeolite cracking catalyst in greater amount than nonzeolite cracking catalyst.

References Cited UNITED STATES PATENTS 10 HERBERT LEVIN'E, Primary Examiner U.S. Cl. X.R.

20s-80, 120, 153, 155, DIG. 2 

